Such a process is described in Advanced Chemical Separations [Homogeneous Catalysis-II, Symp. 1973](1974), 132, 19-26). This article describes a method by which the cobalt is recovered from an organic phase after hydroformylation by mixing the organic phase with a (polar) mixture of diluted acetic acid and water in the presence of air. The cobalt carbonyl is oxidized to Co.sup.+2, ending up in the water mixture as the corresponding salt (similar to step (b) of the invention). After a phase separation between the polar water mixture and the organic phase, the water mixture (similar to step (c)) is subsequently treated with carbon monoxide and hydrogen at a temperature of (150.degree.-200.degree. C.) and a pressure of 30 MPa, upon which cobalt is reduced to cobalt carbonyl (the so-called precarbonylation). This reaction is represented by formula (1): EQU 2Co(OOCCH.sub.3).sub.2 +8CO+3H.sub.2 .fwdarw.2HCo(CO).sub.4 +4CH.sub.3 COOH(1)
After this step the water mixture is contacted with an organic mixture, which mixture forms the feed for the hydroformylation reactor, upon which the cobalt carbonyl passes to the organic phase (similar to step (e)). The water mixture still containing unconverted Co.sup.2+ and the organic mixture are separated by means of phase separation. The organic mixture is subsequently directed to the hydroformylation reactor (similar to step (f)).
A drawback of this known method is that a precarbonylation is needed. The precarbonylation reaction is slow and requires a high pressure, so that use must be made of big reactors that are suitable for high pressures.